1. Field of the Invention
The present invention relates to a novel process for decarbonylating aldehydes and specifically n-aldehydes. More particularly, this invention relates to the decarbonylation of n-butyraldehyde to produce propylene, carbon monoxide and hydrogen, by passing the n-butyraldehyde over a catalyst comprising a metal selected from a group consisting of palladium, platinum, rhodium, copper, silver, gold and zinc supported on or exchanged onto a zeolite. Further, this invention also relates to the decarbonylation of n-aldehydes by passing the n-aldehydes over a catalyst comprising a metal selected from the group consisting of palladium, copper, silver, gold and zinc supported on silica.
2. Description of Art
The hydroformylation of olefinically unsaturated carbon compounds to produce aldehydes is well known. However, the hydroformylation of many of these compounds result in the production of mixtures of both isomeric forms of the aldehydes. For instance, when propylene is hydroformylated, a mixture of normal and isobutyraldehyde is obtained wherein the n-isomer is predominant. Present processes have not been totally satisfactory in providing an economical process for producing primarily the iso form of the aldehyde.
A novel solution for economically producing branched aldehydes and, more particularly, isobutyraldehyde is provided by the process of the present invention. After olefins are hydroformylated to obtain a mixture of normal and branched aldehydes, the n-aldehydes are either decarbonylated after separation from the branched aldehydes or are selectively decarbonylated from the reaction mixture of normal and branched aldehydes to produce predominantly olefins having one less carbon atom than the aldehydes, carbon monoxide and hydrogen. These decarbonylation products are then recycled through another hydroformylation process to produce additional aldehydes. Thus, the process of the present invention provides in part an economical and efficient technique for producing isoaldehydes, such as isobutyraldehyde, by selectively decarbonylating the n-aldehydes and recycling the resulting olefins to the hydroformylation reaction.
Numerous hydroformylation or carbonylation catalysts have been disclosed in the art. For example, U.S. Pat. No. 3,352,924 to Gladrow et al. discloses a carbonylation reaction using crystalline alumino-silicate zeolites containing rhodium and cobalt. U.S. Pat. No. 4,185,038 to Carlock discloses a hydroformylation catalyst comprising rhodium and iridium compounds covalently bound to inorganic oxide polymers such as silica gel, alumina, silica-titania, alumino-silicate and open-lattice clays.
Various decarbonylation catalysts have also been disclosed. For example, U.S. Pat. No. 3,578,423 to Falbe et al. discloses a process for catalytically splitting isobutyraldehyde to produce carbon monoxide and hydrogen in the presence of nickel containing catalysts. U.S. Pat. No. 4,039,584 to Falbe et al. discloses a process for catalytically cleaving isobutyraldehyde to form propylene, carbon monoxide and hydrogen over a supported rhodium and/or platinum catalyst. Other decarbonylation catalysts have been disclosed by U.S. Pat. No. 4,200,589 to Scharf and U.S. Pat. No. 4,262,157 to Hori et al., including catalysts containing mixtures of copper oxide, manganese oxide, zinc oxide and diazabicycloalkenes optionally in the presence of a simple copper salt.
Finally, the use of aluminosilicates, such as zeolites and molecular sieves, to achieve selectivity between a mixture of various compounds based on differences in molecular shapes or sizes is known. For example, U.S. Pat. No. 3,535,398 discloses the use of aluminosilicates for selectively conducting an organic chemical reaction. The process separates straight-chain polar compounds from mixtures of the same with straight-chain non-polar compounds as well as the separation of cis-isomers from trans-isomers.